1. Field of the Invention
This invention relates to a device for gating a blanking bar into a recording of analog signals on the recording section of an image recording device. In particular, this invention relates to a gating device which may be used with an image recording apparatus in connection with patient monitoring.
2. Description of the Prior Art
In a prior known image recording device, the analog signals are supplied by a frame repeat memory at least for a presettable period of time as a frozen waveform with circular updating. A blanking bar dynamically processes through the recording. It separates the signal beginning from the signal end in the signal image.
The frame repeat memory may be an analog memory, which stores the analog signals to be represented directly in analog form and outputs them to the image recording device in this analog form. In a preferred realization, however, the frame repeat memory may be a digital memory, e.g., a dynamic RAM or a dynamic shift register. The analog signal is supplied to the input of this digital memory via an analog-to-digital converter. The digitized signal is delivered to a digital-to-analog converter, the output of which provides the recording signal. The image recording device may be a printer or recorder, e.g., an ink jet recorder. Frequently, an x,y,z oscilloscope is used for recording.
In signal reproduction by means of dynamic repetition, there are, as is known, two possibilities of signal representation:
According to the first possibility, the newest information is always inserted at one end (usually the right end) and the remaining information is displaced towards the other end (usually the left end). In this method it appears if the information is being "scrolled" from one end to the other.
According to the second possibility, the newest information replaces the oldest information at its fixed position on the screen. The display appears "frozen" or "fixed" although the information is changed. In order to show the location in this fixed display of the newest information (or the oldest), a vertical blanking bar is introduced between the two. The traveling vertical blanking bar indicates the boundary between new and old signal information in the memory. It thus shows where the frozen signal has its beginning and where it ends. The creation of a vertical bar in the "fixed mode" method presents no difficulties for the normal application, in which the information is cyclically given out by the frame repeat memory and is sent directly to the display device of the image recording device.
However, problems arise in the use of the "fixed mode" method, when signal images are to be transmitted within a group of recording devices from one device to another, or from one recording device to a central station. Direct transmission of a blanking pulse, which is the basis for a bar indication, is not normally possible as part of the analog y-axis waveform transmitted.
In the relatively narrow low frequency bandwidth of a typical transmission link of a y-axis analog waveform, the leading edge of a fast-rise-time blanking bar pulse will be "degraded" and introduce some misinformation into the analog display. The dynamic response limitations of the transmission link introduce similar degradations and misinformation at the falling edge of the transmitted blanking bar pulse.